Icelandic domains (.is) require that their domains support reverse DNS, which means configuring PTR records on the hosting server.

Is it possible to set up a PTR record for GitHub Pages site hosting?


I have an Icelandic top-level domain - petejones.is - and am using CloudFlare for DNS and GitHub Pages for hosting. Icelandic domains are a little unusual in that .is domains must be registered through the national registrar ISNIC, and they have some tougher (it seems) requirements that the registered domains must comply with.

Apparently my setup is not quite up to snuff, as I've just gotten a notice from them that my DNS is not configured correctly. Here's the key bit:

Test results for "DREW.NS.CLOUDFLARE.COM": The IP address 2400:cb00:2049:########## of nameserver jasmine.ns.cloudflare.com is missing its PTR record or has an incorrect PTR record. The IP address 2400:cb00:2049:########## of nameserver drew.ns.cloudflare.com is missing its PTR record or has an incorrect PTR record. Test results for "JASMINE.NS.CLOUDFLARE.COM":

My sophisticated research (quick googling) indicates that ISNIC is testing to make sure the domain supports reverse DNS - you can resolve the IP from the domain name and vice versa - which seems to be a way of discouraging spam email domains.

Apparently this is configured on the host, rather than the DNS, which makes sense given that the goal is to find the domain from the host.

Is this possible on GitHub Pages? I've seen plenty of info on adding A or CNAME records but nothing about PTR records. I suspect GitHub doesn't get a lot of requests for this because they aren't concerned with email delivery.


The warning that you're seeing there isn't actually about GitHub or GitHub pages at all, but about CloudFlare's name servers.

Personally, I'd argue that accurate PTR on a name server's IPv6 address really isn't a problem, per se - email is going to care about reverse resolution for the mail server, not the DNS server. We know the DNS server is valid for the domain because it's been delegated to; ensuring the owner of the IP space has named it identically is a pointless exercise.

However, CloudFlare would probably be interested in being compatible with the .is registrar's desires; you should drop them a note and they might happily fix.

  • Thanks! Do you believe this CloudFlare article is incorrect (or misleading), then? – peteorpeter Dec 26 '14 at 13:16
  • @peteorpeter That's not applicable - it's talking about hosted DNS, this situation is for the name servers themselves which belong to cloudflare. – Shane Madden Dec 26 '14 at 17:18
  • What is the distinction between "hosted DNS" and "name servers themselves which belong to cloudflare"? Isn't the former composed of the latter? Obviously you aren't dealing with a pro network/systadmin here - your patience is appreciated ;) In related news I've opened a ticket with CloudFlare - will update if I hear back. Thanks again. – peteorpeter Dec 26 '14 at 18:09
  • @peteorpeter Hosted DNS is for zones of yours that are running on their infrastructure - the configuration for their own infrastructure is separate from that. – Shane Madden Dec 26 '14 at 18:11
  • Did you get anywhere with this @peteorpeter? – Leonard Challis Jul 1 '15 at 20:45

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